Baymax Series by Haruki Ueno, 上野 春生

Hiro's a genius, but what he really wants is to be like his inventor big brother, Tadashi--but one day, Tadashi vanishes while saving Hiro's life. The only thing left behind to console the grief-stricken Hiro is Tadashi's last invention, the health-care companion robot Baymax. But the friendship that grows between the gentle bot and the lonely boy is only the beginning of their adventure...

Hiro teams up with Baymax to resolve the mysterious disappearance of his brother and role model, Tadashi. With four reliable friends and an upgraded Baymax by his side, Hiro finally confronts the masked man, the one who holds the key to the truth!! Spurred by his desire for revenge, Hiro corners the masked man,but then something goes wrong with Baymax?! Read the wonderfully miraculous conclusion to the story of a boy and his kindhearted health-care robot!